A novel compensation method of stator flux estimation in low speed region

This paper presents a novel stator flux compensation method in low speed region based on a voltage model with a form of low pass (LP) filtering. In voltage-model-based stator flux estimation, an LP filter is normally used instead of pure integrator to avoid integration drift problem due to DC offset, noise, or measurement error of back electromotive force. But the error between the pure integrator and LP filter causes the magnitude and phase error of stator flux estimation especially in low speed region, and degrades the performance and efficiency of the direct torque control system. The error is analyzed and some simulations are made. To overcome the error, a novel compensation was illustrated in detail, it is based on regulating the cut-off frequency of low pass filter which varies with the frequency of the stator current detected in low speed region. This method has the merits of simplicity and easier to apply in a digital real system. Some simulation and experiment results show that the drive performance is significant improved with the compensation method in low speed region.